What is Meralgia paresthetica (MP)?
Meralgia Paresthetica is a thigh pain condition that develops as a result of problems with a nerve called the lateral cutaneous nerve of the thigh. This nerve supplies sensation to the side and front of thigh. It originates from the spine and travels via the inside of the belly and groin to reach the thigh. Injury or pinching (entrapment) of the nerve can lead to numbness, pain and altered sensation in the area supplied by the nerve and this condition is called Meralgia paresthetica.
What causes this condition?
The most common cause for this condition is pinching (entrapment) of the nerve as it enters the thigh travelling in close relation to a thigh ligament called the inguinal ligament. The angle of the nerve changes as it travels into the thigh making it more liable to get pinched. Your pain specialist can further explain the anatomical details to help you understand the condition better.
MP generally affects one side although in up to 20% of patients both sides may be involved. Men are more likely to have MP with a peak incidence between the age of 40-60 years. It can be challenging to pinpoint the exact cause as to why this condition develops although it has been observed to occur more commonly in association with conditions such as:
Increased abdominal pressure as seen in pregnancy or distension of abdomen due to increased fluid in belly (ascites)
Obesity (BMI> 30)
Tight clothes/ belts in the waist area such as jeans, military armour and police uniforms
Diabetes and other conditions affecting nerves such as alcoholism
Underactive thyroid (Hypothyroidism)
Nerve injury due to seat belt injury or injury associated with surgeries such as hip or back surgery, surgeries requiring bone grafting, keyhole (laparoscopic) hernia repair
Growth/ swelling of the nerve (neuroma)
Difference in the length of the two legs
Activities involving repetitive leg motion for long hours such as walking or cycling. MP is seen associated with sports such as gymnastics, soccer and strenuous exercise, bodybuilding.
What are the symptoms of Meralgia paresthetica?
The main symptoms of this condition include
Pain, burning, aching or stabbing sensation in the front and outer side of the thigh, extending as far as the outer side of knee. This may be accompanied by groin and buttock pain
Altered sensitivity in the front, other side of thigh
Numbness, tingling sensation
Worsening of symptoms with certain positions such as squatting, walking or standing for long hours. Lying down with legs bent towards the tummy (hip flexion) or sitting may help to reduce the symptoms severity.
As this nerve does not control any muscles, there is no muscle weakness.
How is Meralgia paresthetica diagnosed?
In most cases, the diagnosis can be made by the history and examination. Simple tests such as altered sensation in the area supplied by nerve, pressure on the nerve in the groin, moving the hip backwards may reproduce the symptoms and help in establishing the diagnosis. An ultrasound scan can be useful. I have previously identified nerve abnormalities with ultrasound scans prompting other investigations.
Investigations such as MRI scans may be requested to confirm the suspicion or to rule out other conditions with similar symptoms. Other specialist investigations such as nerve conduction studies or neurography are sometimes required. Often an ultrasound guided injection is used to confirm the diagnosis and provide relief.
How is Meralgia paresthetica treated?
This condition has good prognosis and mild cased can resolve spontaneously or with conservative management. The treatment involves lifestyle changes, medications, physical therapy and ultrasound guided injections or radiofrequency treatment. Surgery is rarely required and is considered for chronic refractory cases not responding to other measures.
Lifestyle changes– these include
Avoiding tight clothes and belts
Weight loss (if indicated)
Rest and avoiding activities which provoke the symptoms
Medications. Different types of medications are used including neuropathic medications (painkillers used for nerve pain) and anti- inflammatories.
Ultrasound Guided Nerve Block
The involved nerve can be identified with the help of ultrasound and guided injections can help relieve the pain. It involves injecting local anaesthetics and a small dose of steroid close to the problem site. The combination helps to reduce pain and inflammation. The injection can be performed as an OPD/ day care procedure and it not only helps confirm the diagnosis but can also provide lasting relief. Skilled clinicians can identify individual branches of the nerve. Ultrasound guidance not only helps to ensure accuracy but also minimises the risk of complications.
Ultrasound Guided Pulsed Radiofrequency (PRF) Treatment
In cases where the effect of the nerve block does not last long, this option can be utilised to prolong the pain relief. The procedure involves identifying the nerve under ultrasound guidance followed by placement of a special needle close to the nerve. The needle is connected to a radiofrequency machine which is used to interfere with the pain signals being transmitted by the nerve. This procedure can provide lasting relief and I prefer this option over other options such as neurolysis as it is associated with less complications/ side effects.
Cryoablation
This method involves freezing of the affected nerve to interrupt the pain signals being transmitted to the brain resulting in pain relief. The procedure does not require any cuts or incisions and involves placing a small probe near the affected nerve. A pressurised coolant travels through the probe and creates an ice ball at the tip of the probe thereby freezing the nerve. As the nerve is not damaged during the process it can regenerate without any permanent damage. This procedure can provide prolonged pain relief, usually lasting 6-8 months although some studies have found even longer lasting benefits. If required repeat freezing of the nerves can be performed with good results.
Surgical management. This is rarely required and is considered for non-resolving severe symptoms. The options include
Decompression – this involves releasing the pressure off the nerve
Excision of part of the nerve (neurectomy). This can lead to permanent numbness in the area supplied by the nerve.
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